Landing code on master should not produce a new image

[Armen Zambrano G.]

Currently, almost any code landing on master will produce a new Docker image tagged as latest which all users of the action will immediately start using.

We need to have control as to when releases happen.

We should only release on tag changes as suggested by @asottile-sentry

As you can see, the commits below are not code changing, thus, it should not produce a new image

As a side note, to my surprise, the caching gets invalidated with COPY package.json yarn.lock /action-release :
https://github.com/getsentry/action-release/runs/7567494647?check_suite_focus=true#step:4:51
Before, we used to copy it from the builder image.